This invention pertains to a coal hydrogenation process in which particulate coal is introduced without preheating directly into a reaction zone preferably containing an ebullated catalyst bed, and the coal is rapidly heated and catalytically hydrogenated therein to provide increased percentage conversion and improved yields of hydrocarbon liquid products.
In the present H-Coal.TM. coal hydrogenation process, particulate coal is slurried in a coal-derived recycle oil and the coal-oil slurry is preheated to a temperature near reaction temperature before feeding it into an ebullated bed catalytic reactor. During the preheating step a major portion of the coal dissolves and a large fraction of the initial coal liquefaction product is residual oil containing preasphaltenes and asphaltene compounds. For example, initial liquefaction of Wyodak subbituminous coal produces about 46 W % residual oil (14% preasphaltenes and 32% asphaltenes), and Illinois No. 6 bituminous coal produces about 64 W % residual oil (36% preasphaltenes and 28% asphaltenes). The preasphaltenes are highly unstable species at elevated temperatures, and can decompose thermally in the presence of hydrogen to form asphaltenes while releasing gaseous hydrocarbons and water, but they can also rearrange, aromatize, and even condense to form char. It is believed that at least part of the material that is observed as unconverted coal or char from a coal catalytic reaction process is char formed from preasphaltenes.
Conventional processes for coal liquefaction and hydrogenation which include a thermal treatment step for the coal-oil slurry prior to the catalytic reaction step are generally disclosed in U.S. Pat. Nos. 3,519,555; 3,700,584; 3,791,957 and 4,111,788. Also, U.S. Pat. No. 3,775,071 to Hoffert, et al discloses feeding dry coal in particulate form to a pressurized ebullated bed catalyst reactor, but does not disclose any feed for limiting the temperature of the coal feed during such pressurizing. Other coal hydrogenation processes use diposable catalyst at plug flow conditions and low solvent/coal ratios, such as U.S. Pat. Nos. 4,090,943 and 4,102,775. In these processes, the coal is heated to near the reaction temperature before feeding it into the catalytic reaction zone.
In Flash hydropyrolysis of coal, as disclosed by Schroeder in U.S. Pat. No. 3,030,297, it is stated that 90% conversion of coal to liquid and gas products can be obtained by heating the coal to about 800.degree. C. (1472.degree. F.) in 2-20 seconds at a hydrogen partial pressure of 500-6000 psi. The liquid produced comprises 30%-60% of the coal and is said to be a light aromatic distillate. U.S. Pat. No. 3,960,700 to Rosen, et al discloses contacting Wyoming Big Horn subbituminous coal with hydrogen at 840.degree. F. for 0.5 seconds, and producing 46% benzene, 12% methane, 4% ethane, and 14% char. Kentucky No. 11 coal similarly processed yielded 40% BTX materials. Also, U.S. Pat. No. 3,488,280 to Schulman discloses catalytic hydrogenation of coal with water recycle, wherein coal together with solvent and catalyst are introduced directly into the reactor. Although some work on coal hydrogenation processes utilizing rapid heating of coal with hydrogen have been disclosed in the above listed patents, these processes do not provide for high conversion of the coal and, and thus, further process improvements in rapid heating and catalytic conversion of coal to form increased yields of desirable liquid products are needed.